Cathode



W. P. ZABEL Aug. 16, 1949.

CATHODE Filed June 28, 1946 lnvenfi'ow: I WiLLiam P. ZabeL, 5 WW His A k iror ney.

.on which the cathode issupported;

Patented Aug. 16, 1949 William P; Zabcl,

Cleveland Heights, Ohio; as-

signer to General Electric Company, a, corporation-of New York.

pplicati n. June 28, 1946, SerialNo. 19,927.

My invention relates to electric dischargedevices, and more particularly tocathodes for such devices and methods of: manufacturing the cathodes.

'It'is an object of my invention to provide a cathode Whichis inexpensive and easyto manufacture and; capable of-being handled on automatic' machines for fabrication into the electrodeassemblies of electric discharge devices' It is also an object to provide cathode structures which have desirable. electrical characteristics and are capable of retaining a, copious supply of electron. emissive1material.

A feature of my inventionisthemanufacture of a cathode. in the formof a helical coil composed of a, plurality of wires coiled in parallel or siderby-side relation and provided with short auxiliary coiled ends spaced, from the main body portion of?the..cath de. by a, turn-or twoof wide open pitch to form gaps. in the-coil. When the cathode. is mounted; by securing thev auxiliary coiled ends to lead-in wirestheeaps serve to prevent thezsuspensionpf. activating material (alkaline earth carbonates. for.. example) appliedjto the main; body portionirornrtraveling by capillai'y action;b yondthegan i thereby ke p it on 'theleadeinwiresi, T e:P1.QVision ofthe auxiliary coiled. ends. alsoserves to. p e i dividual wires in. thegaps from; splaying out and tangling with other coilsduring, handling. The said coiled ends also provide for a good connection to the hooks or clamps of the lead-in wires According to another feature of my invention the coil is wound around a mandrel of oval or other flattened shape, preferably two or more mandrels of round wire extending side-by-side. It is thus assured that the individual wires of the multiple coil are retained in axial alignment.

Further features and advantages of my invention will appear from the following detailed description and from the drawing.

In the drawing, Fig. 1 is an elevation, greatly enlarged, illustrating a method of winding multi ple or duplex coils according to my invention; Fig. 2 is an end view of a coil on the mandrels; and Fig. 3 is an elevation, partly in section, of an end of a discharge device containing a mount including a cathode and its supporting elements.

Referring to the drawing, th cathode coils are preferably wound continuously on automatic machinery by windin a pair of tungsten wires I, 2 around a pair of steel mandrels 3, 4. The wires I, 2 are wound with a closed pitch, that is with 3 Claims. (01. 250-27.5)-

tratedin Fig. 3:

or segments 5 constitute .the mai n bod portions of the individual cathodes and are. separated-by shorter lengths liwhich'are ultimately severed at their midpoints to, constitute auxiliary endgsections 6 spaced at, I from, the main body portions 5 by a turn ortwo. of the *Wiresl, 2; The continuous wound coilron-mandrel is heated toset the wires I; 2 and isthengsevered-at points midway ofthe segments fi 'The mandrels 3, 4 are then dissolved in a suitableacid solutionwhich results in arecoil of the turns of the coils to produce acorkscrew or'spiral fluted contour as illus- Af t e r another heat treatment in which strains are completely removeda'nd' the wires are cleaned, the individual cathode coils are mounted by clampingthe auxiliary endsections 6'- in hook portions of lead-in wires 8 extendingfrom a stem 9. 'The leads 8" are then spread apart a small distance to stretch; thecoil so that the turns of th'e pairs of wires; I-, 2'a-re;spacedapart a distance'of approximately-one milwhile there is a hardly perceptible gapbetween the turns of the individual wires I, 2. r

The cathodecoil is-then provided with'an activating coatin or filling'tindicated by dotted lines I0) 'by-applying thereto-a suspension of activating-material such as" alkaline earth carbonates (later broken down to oxides), the suspension being applied to the main body portion 5- of-thecoil, preferably by means of a troughshaped applicatorsuch as that disclosed in Fatthe adjacent turns touching. The longer lengths em 2,363,055, J; Flaws. The gapsl" prevent the suspension from traveling by capillary action to the leads 8 and end coils 6. This is highly desirable because any material deposited at those points is not properly processed upon passage of current through the coil to break down the carbonates to oxides and volatilize the usual binder, with the result that it evolves harmful gases into the bulb II of the electrical discharge device containing the cathode. It is for this reason that I prefer to clamp the coil in the leads 8 at the end sections 6' rather than at the gaps 1 although the latter practicemay be followed if the gaps I are sufiiciently long to insure a spacing of the end turns of the main body portion 5 from the leads 8.

It will be understood that the wires I, 2 may be of different diameter or of the same diameter, and any desired number of wires (as many as seven, for example) may be used. Moreover, a single mandrel of round wire may be used in place of the two mandrels 3, 4 although I prefer the latter because the oval cross section of the coil and its spiral fluted contour insures retention of the individual wires I, 2 in axial alignment. Of course, a single mandrel of non-circular cross section, such as rectangular, may be used in place of two round mandrels. Also, the method of manufacture described above may be applied to a simple coil of one wire (instead or the plurality of wires I 2) to make coils comprising a main body section (like 5) having auxiliary end sections (like 6') spaced apart by gaps (like 1).

It will further be understood that in place of plain wires I, 2 I may employ continuous coils on mandrels, the said mandrels either being made of tungsten and retained in the finished cathode or being made of steel or molybdenum and dissolved out.

The cathodes described herein may be employed in the well known commercial fluorescent lamps which contain a few millimeters of gas (argon) and mercury, with a cathode at each end of the I being 1; mm. long, thepitch being 215 turns per inch.

An alternative design which provides for fast starting of the arc discharge consists of three wires (corresponding to I, 2) of 1.8 mil diameter wound simultaneously on a single 30 mil round mandrel. Similarly, three or more wires may be wound on an oval mandrel (two parallel round mandrels) When using wires I, 2 of difierent diameters a fine strand may be completely hidden by a coarser one by proper nesting of sizes. The result is a small helix secured within the diametrical limits of the larger one. Figuratively speaking, one coil is inside another, yet they are by no means telescoped or separable like a mechanically assembled coil within a coil.

Another advantage of the duplex or multiple type cathode disclosed herein lies in its difierent electrical characteristics from simple coils of one wire. For instance, with a given mandrel diameter, turn proximity, and cathode body length, a duplex or multiple wound cathode made from one size of small wire may have many more turns 4 and difierent mass than a single wire wire size having the and grills cathode of equivalent larger same cold resistance.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A cathode comprising a multiple helical coil of a plurality of individual wires in side-by-side relation, said coil being of oval cross section and being longitudinally twisted to a spiral fluted contour and having integral auxiliary end sections spaced from the intermediate main body portion of the coil by portions of wide open pitch, the main body portion only being coated with electron emissive material.

2. A cathode comprising a multiple helical coil of a plurality of individual wires in side-by-side relation, said coil being of oval cross section and being longitudinally twisted to a spiral fluted contour and being coated with electron emissive material, the adjacent turns of the group of multiple wires being spaced apart approximately one mil and there being a hardly perceptible gap between the individual wires in the group.

3. A cathode comprising a multiple helical coil of a plurality of individual wires in side-by-side relation, said coil being of oval cross section and being longitudinally twisted to a spiral fluted contour and being coated with electron-emissive material.

WILLIAM P. ZABEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,020,001 Schellenger Nov. 5, 1935 2,106,689 Braselton Jan. 25, 1938 2, 41,933 Perrott Dec. 27, 1938 2,145,911 Anderson et al Feb. 7, 1939 2,214,974 Scott Sept. 17, 1940 2,227,602 Platt Jan. 7, 1941 2,247,869 Beers July 1, 1941 2,329,1 8 Inman Sept. 7, 1943 2,371,205 Zabel Mar. 13, 1945 2,373,427 Stickney Apr. 10, 1945 2,422,272 Viehweger June 17, 1947 2,424,518 Stuart July 22, 1947 FOREIGN PATENTS Number Country Date 187,261 Great Britain Oct. 10, 1922 

